1. Field of the Invention
The present invention relates to a liquid crystal compound, and in particular relates to a liquid crystal compound having high dielectric anisotropy.
2. Description of the Related Art
As technology has rapidly developed, various portable electronic products such as mobile phones, laptops, digital cameras, PDA, MP3, MP4, and etc. have become very important in modern day life. Meanwhile, advantages of liquid crystal displays include a small-size, light-weight, and low electricity consumption, and thus they have been frequently used in recent years. In a liquid crystal display, a liquid crystal material, which will affect the performance of a device using the same, plays an important role in the development of liquid crystal displays.
A good liquid crystal material should be, for example, stable toward water, air, heat, and light and have an appropriate dielectric anisotropy (Δ∈), birefringence (Δn), and elastic constant (Kii). An appropriate liquid crystal material can be chosen depending on particular requirements of liquid crystal displays.
Dielectric anisotropy (Δ∈) refers to the difference between a dielectric coefficient in a parallel direction (∈//)O and a dielectric coefficient in a vertical direction (∈⊥). In other words, Δ∈=∈//−∈⊥. Therefore, when ∈//>∈⊥, it is called a positive diamagnetic anisotropy liquid crystal. When ∈//<∈⊥, it is called a negative diamagnetic anisotropy liquid crystal. The value (positive or negative) of the diamagnetic anisotropy determines whether the liquid crystal is parallel or vertical to the electric field and whether light will pass through the liquid crystal layer or not. In addition, the diamagnetic anisotropy of a liquid crystal and driving voltage can be presented by the following formula:
      V    th    =            π      ⁡              (                              K            ii                    Δɛ                )                    1      /      2      
The larger the diamagnetic anisotropy, the lower the driving voltage. Therefore, the liquid crystal display having high diamagnetic anisotropy can work with a lower voltage. However, diamagnetic anisotropies of most liquid crystal materials are smaller than 3.5, which is not satisfactory for modern day liquid crystal display use.
Therefore, a liquid crystal material having high diamagnetic anisotropy is desirable to decrease driving voltage.